The Genetic Regulation of Wood Vessel Anatomical Traits in Populus

AbstractVessel elements are highly lignified, tube-like cells that serve as the primary water transporting conduits in angiosperm wood. These cells stack end-on-end to form larger structures known as vessels, which provide a low-resistance pathway for the movement of water from roots to leaves. The dimensions and distribution of vessels in wood (vessel anatomy) directly influence water transport efficiency, ultimately affecting tree photosynthetic capacity and growth. Vessel anatomy is also a factor that contributes to the vulnerability of trees to drought-induced cavitation, a process that can lead to lethal hydraulic failure. The genetic regulation of wood anatomy and related physiological traits is not very well understood. A detailed review of wood structure, function, drought acclimation, and implications for forest tree survival can be found in Chapter 1 of this dissertation. Chapters 2 to 4 consist of three studies that make use of a unique Populus deltoides × nigra pedigree carrying genomically defined insertions and deletions that generate gene dosage variation. In Chapter 2, we found that all examined wood traits are under genetic control, showing moderate heritabilities ranging from 0.32 to 0.53. We found significant line-dependent trait variation and significant correlations between most examined traits and gene dosage at specific genomic regions. In Chapter 3, we studied whole transcriptome gene expression in wood forming tissues and integrated our analyses with our previous trait-dosage correlations to find putative mechanisms and specific candidate genes related to trait variation. In particular, we found evidence for tree height-independent regulation of vessel traits. Lastly, in Chapter 4 we found evidence of gene dosage-dependent variation in vessel anatomy-related physiological traits, including vulnerability to drought-induced cavitation. Understanding the genetic regulation of vessel traits in wood will be vital for the development of successful mitigation strategies under current and future climate change-related drought